The background to the invention is as follows.
The systems of the present invention are portable, most conveniently of the credit card size, wherein data is recorded in magnetic form; systems of this type with magnetic bubble memories are known, e.g. as described in U.S. Pat. No. 3,786,445 and European Published Patent Applications Nos. 13191 and 13192. The card shown in EPA 13191 contains a pair of memories and two controlling units. Such cards and systems are used purely with digital information, corresponding to numerical codes, such as is required for banking or identification purposes, the input being by means of a key-board, and there has been no prior suggestion of using them for recording analogue information. Cards of such type have the memories arranged so as to allow immediate recall of the data in any portion of the memory.
It is known to store audio information in an electric memory system, but not hitherto in a convenient portable and non-volatile memory unit. U.S. Pat. No. 3,886,189 described a memory based on a ferroelectric capacitor or saturable ferromagnetic reactor of a non-uniform cross-section, but playback from such a memory is destructive of information thereon.
Equipment for the conversion of speech signals to digital form is now well known, and some of this equipment (wave form coders) is suitable for converting music to digital form.
U.S. Pat. No. 4,296,664 describes sound reproduction apparatus in which a decoder converts digital pitch memory elements into analogue form; the memory has eight outputs and the apparatus is not simple and portable as with the system of the present invention.